The field of the disclosure relates generally to motion of ships in bodies of water, and more specifically, to methods and apparatus for predicting ship motion.
Ship motions are affected by local waves, currents, and wind in combination with the ship's speed, direction, loading, weight distribution, hull shape, and other parameters. In order to predict ship motion, it is necessary to know in advance what the wave motions, current, wind, and other environmental conditions are in the vicinity of the ship. Since waves, current, and wind travel at various speeds and directions, and the ship itself may also be under way, it is desirable to monitor these conditions at significant distances away from the ship so that it can be determined in advance if the waves, current, and wind are heading in a direction that will eventually impart one or more motions onto the ship.
Waves and surface currents can be monitored by radar, light detection and ranging (LIDAR) systems, buoys, and satellite imaging systems. Using radar to monitor waves presents a variety of limitations. For example, X-band radar is a short range line-of-sight solution, and is unable to monitor conditions over the horizon. Furthermore, longer range wave activity can be blocked by large closer waves. X-band radar requires a minimum amount of wind-generated surface texture in order to function. High frequency radar can be blurred if the sensor is moving. Slow update rates makes it difficult or impossible to track an individual wave train, and/or determine wave velocity. LIDAR is a line-of-sight optical system and is impaired by cloud cover, fog, and rain. An airborne radar solution or LIDAR could be deployed by UAVs (unmanned airborne vehicles), but such solutions require special platforms and equipment to deploy and recover, as well as being prohibitively expensive to operate.
Traditional buoys need to be moored to the ocean floor to hold station, which is difficult or impossible in deep water, and time consuming even in shallow water, especially if the buoys are to be recovered. Once moored, a buoy cannot be easily moved to a new location. Further, buoys can break loose from their moorings in storms and be lost and/or damaged. Their instrumentation is also subject to degradation and/or vandalism over time.
Satellite imaging systems using visual methods such as cameras or LIDAR are impaired by darkness and cloud cover. Furthermore, satellite payload space and airtime is expensive. Suitable satellite coverage may not be available in some parts of the world.
Wind speed and direction, and rapid changes in temperature, pressure, and humidity are best monitored by local weather instruments, such as anemometers, thermometers, barometers, and hygrometers. These cannot be readily monitored by remote sensors.